A telephone company is asked to provide cable service to a customer whose house is located a $=2$ km away from the road along which the cable lines run. The nearest cable box is located b $=7$ km down the road.

Let b $-$ x denote the distance from the box to the connection so that x is the distance from this point to the point on the road closest to the house. If the cost to connect the cable line is $$500$ per kilometer along the road and $$700$ per kilometer away from the road, where along the road from the point on the road closest to the house should the company connect the cable line so as to minimize construction cost?

$($Use decimal notation. Give your answer to three decimal places.$)$